1. Field of the Invention
This invention relates to fuel cells and high temperature steam electrolysis, and more particularly to apparatus and methods for integrating fuel cell and high temperature steam electrolysis technology.
2. Description of the Related Art
There is a great deal of interest in hydrogen technologies such as fuel cells to reduce emissions and dependence on fossil fuels. Many expect fuel cells to be an important component in establishing a “hydrogen economy.” Unfortunately, the present infrastructure for production, storage, and delivery of hydrogen is currently vastly inadequate to support a hydrogen economy. Furthermore, problems associated with hydrogen production and storage are complicated by the fact that some fuel cell technologies require ultra-high purity hydrogen to operate effectively.
For example, commercial applications of low-temperature proton-exchange-member (PEM) fuel cells, one of the most promising current technologies for use in automobiles, require very high purity hydrogen to operate. Even sub-parts per million of carbon monoxide in the hydrogen, for example, will act as a poison in many PEM fuel cells. Although hydrogen for use in PEM fuel cells may be derived from hydrocarbon fuels, this method of production typically requires complex chemical processing equipment to remove carbon monoxide and/or carbon dioxide to produce hydrogen with sufficient purity for PEM applications. Alternatively, electrolysis may be used to produce high purity oxygen. This method, however, requires both heat and electric power inputs. High temperature steam electrolysis has a reduced electric power requirement, but requires greater thermal input compared to aqueous electrolysis.
Furthermore, society is always searching for more efficient means for producing electricity. Currently, solid oxide fuel cells (SOFCs) provide one promising technology for producing electricity. Unlike the PEM fuel cells discussed above, solid oxide fuel cells are more fuel flexible and are able to utilize both hydrogen and carbon monoxide as fuel to produce electricity. Nevertheless, solid oxide fuel cells, typically operate at much higher temperatures (e.g., at or around 800 to 850° C.) than PEM fuel cells. The higher operating temperature of SOFCs reduces or eliminates the need for expensive catalysts (e.g., platinum) used in PEM fuels cells.
Although the performance of SOFCs continues to improve at temperatures above 800 to 850° C., SOFCs begin to degrade rapidly as operating temperatures increase beyond these levels. As a result, the operating temperature of SOFCs must be carefully controlled to maximize its life and performance. For this reason, airflow rates through SOFCs are generally designed to be significantly higher than what is needed for the electrochemical reaction in order to remove waste heat from the SOFCs. This generally requires expensive heat exchangers to pre-heat the large airflow through the SOFCs. These heat exchangers are typically a large part of the total system cost of conventional SOFCs.
In view of the foregoing, what is needed is an apparatus and method for integrating fuel cell technology with high temperature steam electrolysis technology in a way that increases the efficiency of both systems. Such an integrated system could be used to produce high purity hydrogen and electricity more efficiently than producing them separately. Such a system could also be used to extract significantly more useable energy from hydrocarbon fuels. Further needed is an apparatus and method to reduce the airflow requirements for conventional SOFCs while simultaneously reducing the amount of electricity required to perform high temperature steam electrolysis.